Conventionally, there has been proposed a speaker system that reproduces sound by adding vibration to an acoustic diaphragm by a magnetostrictive actuator (refer to Patent Document 1, for example).
In a speaker system 1, as shown in FIG. 1, a cylindrical acoustic diaphragm 10 formed of an acrylic resin or the like is vertically supported on a discoid base housing 20, and four magnetostrictive actuators 30 are arranged at equiangular intervals in the base housing 20.
In the speaker system 1, a drive rod 35 for each magnetostrictive actuator 30 abuts on a lower end surface 12 of the acoustic diaphragm 10 to drive the magnetostrictive actuator 30 by an audio signal, so that the magnetostrictive actuator 30 adds vibration to the lower end surface 12 of the acoustic diaphragm 10 in a direction perpendicular to the lower end surface 12 of the acoustic diaphragm 10.
The lower end surface 12 of the acoustic diaphragm 10 is excited by a longitudinal wave, which mixes with a transverse wave to be a mixed wave by the propagation of a vibration elastic wave in a planar direction (a direction parallel to the surface) of the acoustic diaphragm 10, whereby a sound wave is radiated in the planar direction of the acoustic diaphragm 10 to form a uniform audio image across the entire height direction of the acoustic diaphragm 10.
Although omitted in this speaker system 1, it is also described in Patent Document 1 that a regular speaker unit is installed in a central opening part of the base housing 20.
In this case, the acoustic diaphragm 10 functions as a tweeter in charge of an upper range of an audible frequency range, and the regular speaker unit functions as a woofer in charge of a lower range of the audible frequency range.
On the other hand, there has been proposed an acoustic device including an active diaphragm provided in a spherical resonator and a passive diaphragm provided in a position facing the active diaphragm of the resonator (refer to Patent Document 2, for example).